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ThermoelectricityPresented By-:
Mohammad Rameez
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ENERGY ROADMAP
100% energy
from power
source
25% effective
power
5% parasitic
losses
30% coolant
40% Heat Losses Can we convert this heat
into some useful energy?
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Introduction
The pioneer in thermoelectrics was a German scientistThomas Johann Seebeck (1770-1831)
Thermoelectricity refers to a class of phenomena in
which a temperature difference creates an electric potential
or an electric potential creates a temperaturedifference.
Thermoelectr ic power generator is a device that
converts the heat energy in to electr ical energy based on
the pr incip les of Seebeck effect
Later, In 1834, French scientist, Peltier and in 1851,
Thomson (later Lord Kelvin) described the thermal
effects on conductors
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Thermoelectricity - known in physics as the
"Seebeck Effect"
In 1821, Thomas Seebeck, a German physicist,
twisted two wires of different metals together
and heated one end.
Discovered a small current flow and so
demonstrated that heat could be converted to
electricity.
Seebeck Effect
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Seebeck Effect
Metal rod
Electron mobility Phonon motion
Photon
Phonon motion
Electron mobility
Electrons in the hot region are more
energetic and therefore have greater
velocities than those in the cold region
dT
dVS
Seebeck Coefficient
Heat transfer through electrons
and phonons (lattice vibrations)
Al Al
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Seebeck Effect
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PELTIER EFFECT
In 1834, a French watchmaker and part time
physicist, Jean Peltier found that an electricalcurrent would produce a temperature gradient atthe junction of two dissimilar metals.
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PELTIER COOLING
>0 ; Positive Peltier coefficient
High energy holes move from left toright.
Thermal current and electric currentflow in same direction.
q=*j, where q is thermal current density and j is electrical currentdensity.
= S*T (Volts) S ~ 2.5 kB/e for typical TE materials
T is the Absolute Temperature
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PELTIER EFFECT
Peltier Effect Thermoelectric
Cooler Diagram:
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PELTIER EFFECT
Peltier Effect Animation:
As current passes through the 1st plate, the negative electrons and positive holes(called carriers) transport the heat making the 1st plate to be warm (heat isabsorbed) and the 2nd plate to be cold (heat is released).
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THOMSON EFFECT
Discovered by William Thomson (Lord Kelvin)When an electric current flows through a conductor, the
ends of which are maintained at different temperatures,
heat is evolved at a rate approximately proportional to the
product of the current and the temperature gradient.
dx
dTI
dx
dQ
is the Thomson coefficient in Volts/Kelvin
Seebeck coeff. S is temperature dependent
dT
dSTRelation given by Kelvin:
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THE SEEBECK EFFECT:
EMF caused by temperaturegradient across two dissimilarconducting metals, whichform a closed loop.1
THE PELTIER EFFECT:
Temperature differentialcaused at the junctions ofdissimilar conductors, withthe passing of current.1
THE THOMSON EFFECT:
Electrical current causedby a temperature gradientin a single homogeneousconductor. 1
THERMOELECTRIC EFFECTS(SUMMARY)
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2S
z
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Efficiency of Thermoelectric Devices
Desirable > 0.2
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EFFICIENCY OF THERMOELECTRIC DEVICES
The Figu re of Meritof a thermoelectric material
S= Seebeck coefficient
= Electrical conductivity
ke= Electronic contribution to thermal conductivity
kp= Phonon contribution to thermal conductivity
Tkk
SZTpe
2
Conflicting Issues in Design:
Increasing (through increase in n) reduces S
Increase in accompanied by an increase in eIncreasing effective mass m*: increase in S, but decrease in
Attempts to change p interferes with changes in (mobility)
Metals: S ~ 10 V/K, Semiconductors: S ~ 100 V/K
Degenerate semiconductors, heavy atoms, soft spring constants ofbonds: Bi2Te3 and its alloys
*
2
mne
3
2
2
2
B
2
)3n
(m3eh
Tk8S
m*/(n1/3[k/])
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Thermoelectric materials
The good thermoelectric materials should possess
1. Large Seebeck coefficients
2. High electrical conductivity
3. Low thermal conductivity
The example for thermoelectric materials
BismuthTelluride (Bi2Te3), Lead Telluride (PbTe),
SiliconGermanium (SiGe),
Bismuth-Antimony (Bi-Sb)
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LT
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THERMOELECTRIC EFFECT IN SEMICONDUCTORS
Thermoelectric power generation is explained by a gradient in conduction band energy, across a
material. This gradient in conduction band energy is caused by an applied thermal gradient.
For homogeneous materials the conduction band energy is directly related to temperature.
Electrons on the hot side of a material have greater conduction band energy than those on the
cold side producing an EMF.3
e
e
ee
e
e
3. http://ecee.colorado.edu/~bart/book/
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THERMOELECTRIC EFFECT IN SEMICONDUCTORS
h
h
hh
h
h
Ev
EC
e
e
ee
e
e
As for conduction band energy, valence band energy is also varied across a material with anapplied thermal gradient. In this case, valence band carriers are termed holes, and correspond to
an absent electron.3
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e
e
e
e
e
e
THERMOELECTRIC EFFECT IN SEMICONDUCTORS
e
e
ee
h
h
h
h
h
h
h
h
hh
n-type Materials
For n-type materials, electrons are the primary charge carriers for which appliedthermal gradients produce an EMF in the direction shown above.3
p-type Materials
For p-type materials, holes are the primary charge carriers for which appliedthermal gradients produce an EMF in the direction shown above.3
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e
e
e
e
e
e
THERMOELECTRIC EFFECT IN SEMICONDUCTORS
h
h
h
h
h
h
n-type Material
p-type Material
L
OAD
+
-
When connected in series, the two materials produce thermoelectric power capable of powering aload.
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MATERIAL OF CHOICE FOR THERMOELECTRICITY
TE Parameters
Materials
Metals
Insulators
Semiconductors
Semiconductors most suitable TE material.
Allow separate control of G (electrons) and (phonons).
Electrical
Conductivity(G)
Seebeck
Coefficient(S)
Thermal
Conductivity()
High~102 W/m-K
High
Moderate10-3S/m
High~120 V/K
Very High~107 S/m
Low~ 10V/K
Low~10-2-10-4 W/m-K
Low~10 W/m-K
Extremely
low (~10-10S/m)
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Conventional Thermoelectric Materials
Optimized Bi2Te3 though Sb/Se substitution
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POTENTIAL ZENHANCEMENT IN LOW-DIMENSIONAL MATERIALS
Increased Density of States near the Fermi Level:
high S2(power factor)
Increased phonon-boundary scattering: low
high Z = S2/:
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THIN FILM SUPERLATTICE THERMOELECTRIC MATERIALS
Thin film superlattice
Approaches to improve ZS2/:
--Frequent phonon-boundary scattering: low
--High density of states nearEF: high S2in QWs
Quantum well
(smallerEg)Barrier(largerEg)
Incidentphonons Reflection
Transmission
Phonon (lattice vibration wave)
transmission at an interface
Interface
LOW DIMENSIONAL THERMOELECTRIC MATERIALS
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LOW-DIMENSIONAL THERMOELECTRIC MATERIALSThin Film Superlattices of
Bi2Te3,Si/Ge, GaAs/AlAs
Ec
Ev
x
E
Quantum wellBarrier
Top View
Nanowire
Al2O3 template
Nanowires of
Bi, BiSb,Bi2Te3,SiGe
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THERMOELECTRIC PROPERTIES OF THIN-FILM MATERIALS
USED FOR THERMOELECTRIC MICROSENSORS
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THERMOELECTRIC DEVICES
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SEMICONDUCTOR PELTIER COOLERS
Bismuth-Telluride n and p
blocks
An electric current forces
electrons in n type and holes in ptype away from each other on the
cold side and towards each other
on the hot side.
The holes and electrons pull
thermal energy from where theyare heading away from each other
and deliver it to where they meet.
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Electrical Power Generation and Cooling
Wasted heat to electricity
Environment-friendly
No moving parts: easy maintenance
Long life
Precision control of T with spatial resolution
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THERMOELECTRIC MEMS DEVICES
The miniaturisation and development of MEMS based
thermoelectric devices has the potential to improve the
performance of thermoelectric devices, and create new
applications for the technology. Thermoelectric MEMS based
devices, based on thin-film technology, that are compatiblewith modern semiconductor processing techniques have
now started to enter the market place.
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THERMOELECTRIC MICRO POWER GENERATORS
Miniaturized, fully-integrated, monolithically
and batch-fabricated thermoelectric power
generator capable of powering MEMS devices
Sufficient power (individually or in small
arrays) to replace batteries in macroscale
systems such as weapons,man-portablecomputers, radios, and GPS receivers
Thermocouple probe
Micromachined scanning thermocouple
probe for high resolution temperaturemapping, topographical mapping, surface
imaging
e.g. for ULSI diagnostics
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APPLICATIONS
Deep space probes
Microprocessor cooling
Laser diode temperature stabilization
Temperature regulated flight suits
Air conditioning in submarines
Portable DC refrigerators
Automotive seat cooling/heating
Radioisotopic Thermoelectric
Generator (RTG)
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Some Applications of Thermoelectrics
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APPLICATIONSWater/Beer Cooler
Cooled
Car Seat
Electronic Cooling
Cryogenic IR Night Vision
Laser/OE Cooling
TE
Si bench
AUTOMOBILE
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In ATEGs, thermoelectric materials arepacked between the hot-side and the cold-
side heat exchangers. The temperature
difference between the two surfaces of
thethermoelectric module(s) generates
electricity.
Thermoelectric generator in a Volkswagen
Golf Plus lowers fuel use by 5% .
AUTOMOBILE
http://en.wikipedia.org/wiki/Heat_exchangershttp://en.wikipedia.org/wiki/Thermoelectricityhttp://en.wikipedia.org/wiki/Thermoelectricityhttp://en.wikipedia.org/wiki/Heat_exchangers -
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Thermionic Watch absorbs heat fromthe wrist and dissipates it through thefront side of the watch. The internalthermoelectric generator converts thetemperature into electricity and drives thewatch. The heat powered Thermicwatches utilizes heat energy
continuously while wearing on the wrist.The memory chip inside the watch willkeeps tracks of time even when not incontact with the body.
The Seiko watch Introduced in 1988 .
under normal operation the watchproduces 22W of electrical power. With
only a 1.5K temperature drop across theintricately machined thermoelectricmodules, the open circuit voltage is 300mV, and thermal to electric efficiency isabout 0.1%.
BIO WATCHES (THERMIC WATCHES)
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